Vacuum treatment system and process for manufacturing workpieces

ABSTRACT

A process is disclosed for manufacturing coated substantially plane workpieces, in which the workpieces are guided to a vacuum treatment area guided by a control. The treatment atmosphere is modulated in the treatment area as a function of workpiece position with the defined profile. The system and process can be used to deposit defined layer thickness distribution profiles on substrates in a reactive coating.

BACKGROUND OF THE INVENTION

This application claims the priority of Swiss application 964/99, filedin Switzerland on May 25, 1999, the disclosure of which is expresslyincorporated by reference herein.

In such control systems, the control quantity (ACTUAL value measurement)is detected by measuring the plasma light emission, for example, in thecase of a specific spectral line, by measuring the target voltage. ADESIRED value is defined for the measured control quantity and,corresponding to the control deviations, for example, the flow ofreactive gas, in the above-indicated example, the oxygen flow (or, if itis not detected as a control quantity, the target voltage) is set as aregulating quantity in the control circuit. As a result, the operation,particularly a stabilization of the process in the desired workingpoint, for example, in the above-mentioned transition mode, is achieved.

FIGS. 1 to 4 are schematic views of typical vacuum treatment systems ofthe latter type. They are systems of this type and workpiecemanufacturing processes which can be implemented by vacuum treatmentsystems of this type and at which the problems to be described wererecognized and solved according to the invention. The solutionsaccording to the invention can, however, basically be used for systemsand processes of the initially mentioned type in which the treatmentprocess or the treatment atmosphere is controlled.

As illustrated by the arrow 4, substrates 1 are moved in a workpiececarrier drum 3 rotating in a treatment chamber past at least onesputtering source 5. The sputtering source 5 with the metallic, thuselectrically highly conductive target is, normally constructed as amagnetron source, DC-operated; often additionally with a chopper unitconnected between a DC feeder generator and the sputtering source 5, asdescribed in detail in EP-A-0 564 789, also incorporated by referenceherein. A chopper unit intermittently switches a current path situatedabove the sputtering source connections to be of high resistance and lowresistance.

In FIGS. 1 to 4, the DC generator and the optionally provided chopperunit are each illustrated in the blocks 7 of the sputtering source feed.In addition to a working gas G_(A), such as argon, a reactive gas G_(R),such as oxygen O₂, is admitted to the treatment atmosphere U of thevacuum chamber, the reactive gas G_(R) particularly by way of gas flowregulating valves 10.

Above the sputtering sources 5, a reactive plasma 9 is formed in whichthe substrates and workpieces 1 moved through by the drum 3 above thesputtering surfaces are sputter-coated. Because not only the substrates1 are coated with the electrically poorly conductive reaction productsformed in the reactive plasma 9 but also the metallic sputteringsurfaces of the sputtering sources 5, the coating process described sofar, particularly for achieving coating rates which are as high aspossible, is unstable. For this reason, particularly in the case ofthese treatment processes and systems, the treatment process and, inthis case, actually the treatment atmosphere acting upon the workpieces1, is stabilized in the treatment area BB with a control.

As a possible implementation embodiment of such a control circuitaccording to FIG. 1, a plasma emissions monitor 12 measures theintensities of at least one of the spectral line or linescharacteristics of the light emission from the reactive plasma 9. Theseintensities are fed as a measured control quantity X_(a) to a controller14 _(a).

In FIG. 2, the target voltage on the sputtering source 5 is measured asthe measured ACTUAL quantity Xb of the control circuit by a voltagemeasuring device 16 and is fed to a controller 14 b. With respect to thedetection of the measured control quantity X, FIGS. 1, 3 and 2, 4correspond to one another. At the controllers 14 a and 14 b, for formingcontrol differences, the respective measured control quantities Xa andXb are compared with the preferably adjustable guide values Wa and Wb,which correspond to the measured control quantities.

In accordance with the formed control differences at the controllers 14a and 14 b and their amplification on transmission paths (notillustrated separately) dimensioned with respect to the frequencyresponse according to the rules of control engineering, regulatingsignals S are generated at the output side of the controllers 14. Asseen in FIGS. 1 and 2, the regulating signals, correspondingly markedSaa and Sba, are guided to the flow control valves 10 for the reactivegas as regulating elements which are set such that the respectivelymeasured control quantities Xa and Xb are led to the values defined bythe guide quantities Wa and Wb and are held there.

As seen in FIGS. 3 and 4, the regulating signal generated on the outputside of the controllers 14 a and 14 b, which is correspondingly markedSab and Sbb, is fed to the sputtering source feeds 7 which nowthemselves act as control regulating elements. This takes place eitherat their DC generators and/or at their optionally provided chopperunits, where the chopper duty cycle is set.

The systems illustrated, for example, by FIGS. 1 to 4 are thereforevacuum treatment systems with a vacuum chamber, having elements forestablishing a treatment atmosphere (specifically particularly asputtering source and reactive gas feeds), and a sensor arrangement fordetecting the treatment atmosphere momentarily existing in the chamber,the plasma emissions monitors and voltage measuring devices described asexamples. The sensor arrangements ACTUAL-value sensors of at least oneof the mentioned elements form a regulating element of one controlcircuit respectively for the treatment atmosphere.

For depositing electrically poorly conducting or non-conductive layersby way of the release of one layer material component of electricallyconductive targets, an approach described in U.S. Pat. No. 5,225,057involves first carrying out the metallic coating in spatially separatedtreatment stages and then oxidizing it in a reactive gas stage (anoxidation stage). In this known approach, there is no stability problemwith respect to the coating process, but the system configurationconsisting of several stages used for this purpose is relativelycomplicated.

As mentioned above, the present invention is based on treatment systemsand manufacturing processes of the type explained by reference to FIGS.1 to 4. It was demonstrated there that, particularly in the case of widesubstrates of a width B larger than the dimension A in the samedirection, preferably five times larger, and/or in the case of a smalldiameter of the substrate drum 3, along the substrate width B, becauseof the non-linear movement of the substrates in the area BB and relativeto the sputtering source 5, a pronounced, approximately parabolic layerthickness distribution is obtained, as illustrated in FIG. 11 a. Thislayer thickness distribution is known as a so-called “chord effect”.

The effective width of a substrate is its linearly measured dimension inthe direction of its relative movement to the sputtering source 5. Thecorresponding effective sputtering source dimension A is its linearlymeasured dimension in the same direction. Furthermore, theabove-mentioned substrate width B can definitely be taken up by severalside-by-side smaller substrates. The addressed substrate 21 will thenactually be a batch substrate.

In addition, it is stressed at this point that, for example, with a viewto FIG. 1, the substrates may definitely be arranged on the interiorside of a revolving carousel, which revolves around a sputtering sourcearrangement on a path which will then be concave with respect to thesputtering source arrangement. All foregoing statements and allfollowing statements which are based on the drum arrangements accordingto FIGS. 1 to 4 analogously apply to the full extent to concaveworkpiece movements with respect to the sputtering source.

SUMMARY OF THE INVENTION

An object of the present invention is to implement, independently of themovement path and movement alignment of the workpieces moved in thetreatment atmosphere, a desired layer thickness distribution in atargeted manner.

In a relevant vacuum treatment system, this object has been achieved inthat at least one of the elements for establishing the treatmentatmosphere, as a function of the workpiece carrier position, modulatesthe treatment atmosphere in the treatment area according to a givenprofile. Also, such a system or the related process, the control, forexample, for stabilizing the treatment process, holds the treatmentatmosphere in a DESIRED condition or working point. In contrast to U.S.Pat. No., according to which, by the variation of the sputteringperformance when depositing metallic layers, action is taken against thechord effect, in the present invention, a control resists a change ofthe treatment atmosphere.

In a first currently preferred embodiment of the vacuum treatment systemaccording to the present invention, an adjustable DESIRED value definingunit is provided on the control circuit, as explained by reference toFIGS. 1 to 4, and the modulation provided according to the invention isimplemented synchronously with the substrate movement by modulation ofthe DESIRED value.

In a further currently preferred embodiment of the systems according tothe invention, the provided control is carried out more slowly than thetreatment atmosphere modulation carried out according to the invention.Accordingly, the control of the “disturbance variable” modulation cannottake place in a settling manner. The modulation introduced according tothe invention, with respect to control engineering, is therefore theintentional introduction of a disturbance variable which is not to besettled.

If, as in the preferred system which is explained in FIGS. 1 to 4, thevacuum chamber comprises a sputtering source with an electricallyconductive target and if a reactive-gas tank arrangement is connected tothe chamber which reactive-gas tank arrangement has a reactive gas whichreacts with the material released by the sputtering source to form amaterial with an electrically poorer conductivity as the coatingmaterial, the modulation preferably takes place at the electric sourcefor the feeding of the sputtering source (its current or power), either,in the case of the preferred DC feeding, on the DC generator itselfand/or at a chopper which is connected between the DC generator and thesputtering source and whose duty cycle is established.

In a further preferred embodiment, the system according to theinvention, as a moved workpiece carrier, has a rotatingly driven carrierdrum with workpiece receiving devices distributed on its periphery. Themodulation is then synchronized with the drum revolving movement and isapplied with a repetition frequency which corresponds to the workpiececarrier passing frequency.

Furthermore, a modulation form memory unit is preferably provided on thesystem according to the invention. This memory unit has at least one,preferably several previously stored modulation courses as well as aselection unit for the selective adding of the respectively desiredmodulation curves to the mentioned regulating element.

The process according to the invention of the initially mentioned typefor manufacturing workpieces is characterized in that the treatmentatmosphere in a treatment area of the workpiece moving path is modulatedas a function of the workpiece position by a given profile.

The system according to the invention as well as the process accordingto the invention are particularly suitable for establishing ahomogeneous layer thickness distribution on plane substrates ofdiameters B larger than the effective dimension A of the sputteringsource or for producing defined layer thickness distributions onsubstrates, thus particularly also on substrates which are not plane. Inaddition, the present invention basically relates to processes forproducing substrates, in which the chord effect is compensated on thesubstrates which are moved past the sputtering source on a circular pathwhich is convex or concave with respect to a sputtering source.

The above-mentioned U.S. Pat. No. 5,225,057 also teaches modulating thesputtering performance of metallic targets for the compensation of theabove-mentioned chord effect, specifically such that, in the case ofsubstrates which are situated centrically with respect to the sputteringsource, the sputtering performance passes through a maximum. Moreprecise tests have indicated, however, that this type of modulation isnot capable of compensating the addressed chord effect. Surprisingly, aswill be demonstrated, the sputtering performance of the source must bemodulated as a function of the substrate position such that, in the caseof substrates situated centrally with respect to the sputtering source,the sputtering performance passes through a minimum.

Furthermore, manufacturing processes according to the invention aredisclosed which particularly effects of the above-mentioned chordphenomenon, relative to a substrate movement which is convex or concavewith respect to the sputtering source, are eliminated by a modulation ofthe reactive gas flow—in the preferably used reactive coatingprocesses—and/or the working gas flow, i.e., the flow of an inert gas.

With respect to the modulation of the sputtering performance and aconcave moving path of the substrates with respect to the sputteringsource, when the workpieces are situated centrically with respect to thesputtering source, the sputtering performance is preferably modulated toa maximum.

Correspondingly, when the moving path of the substrates is convex withrespect to the sputtering source, the reactive gas flow is modulatedsuch that, with workpieces situated centrically with respect to thesputtering source, this flow passes through a maximum and if, incontrast, the substrate moving path is concave, it passes through aminimum.

If the working gas flow alone or in combination with the other definedmodulation quantities is modulated according to the invention, thispreferably takes place in such a manner that, in the case of a convexmoving path of the substrates with respect to the sputtering source,while the workpieces are situated centrically with respect to thesputtering source, the working gas flow passes through a minimum, but,when the moving path is concave, it passes through a maximum.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1–4 are schematic views of the prior art.

FIG. 5 is a schematic view of a treatment system and process accordingto the invention;

FIG. 6 is a schematic view similar to FIG. 5 of a first embodiment ofthe modulation according to the invention;

FIGS. 7 to 10 are views similar to FIGS. 1 to 4 of further embodimentsof the systems and corresponding manufacturing processes of theinvention according to FIGS. 1 to 4;

FIG. 11 is a qualitative view with a curve (a) of a layer thicknessdistribution on substrates if they are manufactured according toprocesses and systems according to FIGS. 1 to 4; curve (b) in the caseof the modulation according to the invention selected for an optimallayer thickness homogeneity; curve (c) in the case of anovercompensation with the modulation according to the invention; and

FIG. 12 is a qualitative view of the modulation signal according to theinvention applied to the systems shown in FIGS. 7 to 10 in order toachieve layer thickness distributions on the substrates according toFIG. 11( b) or, shown by a broken line, according to (c).

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 5, an “x” illustrates the moving path for a workpiece 20 whichis to be treated inside a vacuum treatment chamber (not shown). Themomentary position of the workpiece 20 along the moving path x is markedxs. Inside the treatment chamber, the workpiece 20 is treated in atreatment area BB in a treatment atmosphere U.

For producing the treatment atmosphere U, elements are provided in thetreatment chamber or operatively connected with it which are generallyillustrated in FIG. 5 by block 22. Such elements may be formed, forexample, by controllable valve arrangements for gas inlets into thetreatment chamber, particularly reactive gas inlets and/or working gasinlets, electric supply voltages for plasma discharge paths, heating orcooling elements, magnet arrangements for generating magnetic fields inthe chamber. A sensor arrangement 24 is provided to measure one orseveral characteristic quantity(ies) of the treatment atmosphere U inthe treatment area BB. On the output side, the sensor arrangement 24 isoperatively connected with a subtraction unit 26 to which it feeds ameasured control quantity signal X. In addition, the DESIRED valuesignal W is fed to the subtraction unit 26 by a preferably adjustableDESIRED value defining unit 28. The control difference obtained at thesubtraction unit 26 is fed as the regulating element by way of acontroller 30 or amplifier to at least one of the elements influencingthe treatment atmosphere U.

To this extent, in a general way, the description of FIGS. 1 to 4corresponds to FIG. 5 as well. According to the invention, asschematically illustrated by the position detector 34 in FIG. 5, themomentary position xs of a workpiece 20 to be treated is now detectedand followed. The output signal of the detector arrangement 34 triggersa modulation signal M at a modulation unit 32 which varies with theposition Xs. The modulation signal M is fed to at least one of theabove-mentioned elements in block 22 according to FIG. 5 which alsodetermine the treatment atmosphere U. As a result, the treatmentatmosphere U in the treatment area BB is changed in a targeted mannercorresponding to the modulation signal M so that, when passing throughthe treatment area BB, the workpiece 20 is treated corresponding to theselected modulation M with a desired treatment profile along its surfaceto be treated.

A first form of implementing the modulation according to the inventionis obtained in that the modulation, as illustrated in FIG. 6, is appliedto the command variable W of the control circuit and thus the controlcircuit regulating element is also used for the application of thedesired modulation to the treatment environment U.

FIGS. 7 to 10 illustrate described preferred system configurationsaccording to FIGS. 1 to 4, which, however, are further developedaccording to the invention. On the drum 3, according to FIG. 7, forexample and preferably, a rotating-angle receiver 36 is used as theposition detector 34. The rotating angle receiver 36, by way of therotating position signal 4 s, synchronizes the output of the modulationsignal M(4 s) on the modulation unit 38 with the drum movement and thusthe substrate movement. Preferably, an element for the adjustment of thetreatment atmosphere U is guided by the modulation signal M(4 s), whichelement is not used as a regulating element of the control circuit.

In the stabilization control of the process implemented in the preferredembodiment, which is necessary in order to deposit on targets conductingin the transition mode poorly conducting or non-conductive coatings bymeans of reactive gas, on the one hand, the process stability and, onthe other hand, the reach-through of the provided modulation M(4 s) tothe process atmosphere is ensured. That is, preferably the frequencyresponse of the control circuit is adapted by providing filters 44,preferably low-pass filter or band pass filters, most preferably in thepath of the measured control quantity.

In the preferred embodiment according to FIGS. 7 to 10, the modulationtakes place cyclically corresponding to the substrates 1 which in eachcase travel past the sputtering source 5. In this case, the repetitionfrequency of the periodic modulation signal is normally higher than theupper limit frequency of the closed control circuit. Thus, typicalreaction times of the illustrated process control are in the range of afew hundred milliseconds to several seconds while, as the result of therotating speed 4 of the drum and the number of provided substrates 1,the periodic modulation synchronized with the drum movement has a higherrepetition frequency.

As illustrated in the embodiment of FIG. 9, instead of a rotating anglereceiver 36, as illustrated in FIGS. 7, 8 and 10, a position detector 40can detect the reaching of previously defined substrate positions on thedrum periphery.

As further illustrated in FIGS. 9 and 10, one, preferably two or moremodulation curve forms are previously stored on the modulation unit 38and are selectively activated by a selection unit 42 for the respectiveprocessing method. The various previously filed modulation curve formsallow different substrate treatments at the same system can also betaken into account.

As also illustrated in FIGS. 7 and 8, the modulation used according tothe invention can take place by the modulation of the inert gas orworking gas flow GA, alone or optionally in combination with thecorresponding modulation of other suitable process quantities, such asthe reactive gas flow, the sputtering performance, etc.

In addition, FIGS. 9 and 10 have a dashed line which represents the factthat the modulation used according to the invention can also beimplemented by way of the regulating element used for the control,namely the sputtering performance 7. This modulation takes place moreslowly than provided by the reaction time of the closed control circuit.

The approach according to the invention is used particularly preferablyfor reactive coating processes, particularly in the manufacture ofoptical components. It is surprising that, by using the modulationaccording to the invention, high layer qualities and layer profiles areachieved which are suitable for optical components. The approachaccording to the invention is used in particular if the initiallydefined width B of the substrates or of a substrate batch is larger thanthe assigned sputtering source dimension A, preferably significantlylarger, particularly, five times larger.

In FIG. 11, the curve (a) qualitatively shows the layer thicknessdistribution applied to a plane substrate according to FIGS. 1 to 4 bysputtering from the source 5, specifically independently of whether thedepositing of target material layers in the metallic mode is involved orthe depositing of layer materials reacted in the intramode or transitionmode to electrically non-conductive layers. As the result of amodulation (M4s) according to FIGS. 7 to 10 and as illustrated in FIG.12, the curve (a) of FIG. 11 can be precisely compensated. A layerthickness distribution is obtained on the substrates, as illustrated bycurve (b) in FIG. 11. With an overcompensation by means of the usedmodulation, as illustrated, for example, in FIG. 12 by a broken line, alayer thickness distribution is obtained which is indicated in FIG. 11at (c). At points P1, P2 . . . of FIG. 12, the modulated treatmentatmosphere passes through an intensity minimum. At that minimum, therespective substrates 1 are situated in a centered manner with respectto the sputtering source. In the transition from the convex moving pathto the concave moving path with respect to the sputtering source, thepreferably used minimum/maximum assignments of the modulations are, ofcourse, inverted.

It was therefore recognized in discovering the present invention that,in systems of the type illustrated in FIGS. 1 to 4, also during thesputter coating in the metal mode (i.e., without reactive gas), thechord effect can be compensated by minimizing the sputtering performanceif the substrates are situated in a centered manner above the sputteringsource.

As a result, an optimal uniformity of the layer thickness over thesubstrate width B is obtained, which is significant, for example, withsubstrate widths of at least 12 cm. In this case, the adaptation of themodulation curve forms permits the achievement of targeted desiredtreatment distributions, in the preferred case, coating distributions.Mechanical imprecisions of the system configuration, for example, ofsubstrate carriers, can be compensated by correspondingly designedmodulation forms.

If desired, it is also within the contemplation of the presentinvention, in the workpieces which are simultaneously provided on thedrum 3 and which, however, are to be coated with different layerthickness distributions, to add respective different modulation curveforms. For example, meters (not shown) will then detect which of thesubstrates are momentarily moving into the treatment area BB of thesputtering source, and the correspondingly pertaining modulation curveform is activated by the selection unit 42.

According to the present invention, the layer thickness distribution isadjusted in a targeted manner on the substrates moving past. Thisfeature makes possible reduction of the precision requirements on thetreatment system, particularly with respect to its workpiece carrier andprecise positioning of the sputtering source. Undesirable layerthickness distributions which are the primary result are compensated bythe modulation according to the present invention.

Furthermore, in a targeted manner, certain desired layer thicknessdistributions and profiles, for example, for gradient filters, can alsobe implemented. An important aspect of the present invention is also thecoating of substrates which are not planar, such as lens bodies, with auniform layer thickness distribution.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for manufacturing coated substantially plane workpieces,comprising guiding the workpieces to a vacuum treatment; moving theworkpieces past a sputtering source on a circular path which is convexwith respect to the sputtering source; and modulating the sputteringperformance of the source as a function of workpiece position so that,whenever a respective workpiece is located centrally facing thesputtering source, the sputtering performance passes through a minimum.2. The method of claim 1, wherein said workpiece are coated with a layerof substantially uniform thickness distribution.
 3. The method of claim1, further comprising controlling said sputtering performance tocompensate for a chord effect caused by said plane workpiece being movedon said circular path.
 4. A method for manufacturing coatedsubstantially plane workpieces, comprising guiding the workpieces to avacuum treatment; moving the workpieces past a sputtering source on acircular path which is concave with respect to the sputtering source;and modulating the sputtering performance of the source as a function ofworkpiece position so that, whenever a respective workpiece is locatedcentrally facing the sputtering source, the sputtering performancepasses through a maximum.
 5. The method of claim 4, wherein saidworkpiece are coated with a layer of substantially uniform thicknessdistribution.
 6. The method of claim 4, further comprising controllingsaid sputtering performance to compensate for a chord effect caused bysaid plane workpiece being moved on said circular path.